The present invention relates to a throttle control for an internal combustion engine and used for controlling an opening of a throttle valve by driving an actuator in accordance with a depression position of an accelerator pedal. More particularly, the present invention relates to a throttle control which performs a restoration or limp-home operation in the event of a system failure.
A conventional throttle control apparatus employed in an internal combustion engine (electronic throttle system) for controlling an opening of a throttle valve drives an actuator in accordance with the depression position of an accelerator pedal. The throttle control apparatus controls the amount of intake air supplied to the internal combustion engine by opening and closing the throttle valve in an operation to drive the actuator in accordance with a signal generated by an accelerator position sensor for detecting a position of an accelerator corresponding to the depression position of the accelerator pedal.
As is generally known, the electronic throttle system has a fail-safe function which is used for preventing an engine speed of the internal combustion engine from abruptly rising by temporarily cutting off a current supplied to the actuator when some abnormalities or failures occur in the electronic control system.
In case occurrence of a failure is once detected in the electronic throttle system but later the failure detection is determined to be an erroneous detection attributed to sensor noise or the like, it is desirable to resume a supply of a current to the actuator and to restore the control after verification of a normal operation.
A driver encountering an abnormal condition like the above one may possibly depresses the accelerator pedal a plurality of times without regard to an operating condition that exists at that time in an attempt to grasp an abnormal condition. Thereby, with the accelerator pedal depressed, the engine speed of the internal combustion engine rises abruptly when the electronic control system is restored from the abnormal condition to the normal condition. As a result, it is likely that a vehicle performs an improper operation.
It is proposed in JP-A-6-249015 to reduce the number of operating cylinders of the internal combustion engine to decrease the output of the internal combustion engine in the event of occurrence of failure. Thus, a vehicle is enabled to be driven in a limp-home operation manner.
However, the limp-home operation becomes impossible even if only one of the accelerator position sensor and the throttle angle sensor fails. In addition, the limp-home operation also becomes impossible in the event of a throttle control failure wherein the throttle valve can not be closed even after a predetermined period of time has elapsed since restoration of the accelerator pedal.